1. Field of the Invention
The present invention relates to a light source device, and more particularly, it relates to a light source device which illuminates a target to be imaged by an imaging unit.
2. Description of the Related Art
A so-called fiber light source combining a small-size light source and an optical fiber has been generally known. Such a fiber light source is suited to illumination within a thin structure. As an example of the utilization of a light source device that uses such a fiber light source, Jpn. Pat. Appln. KOKAI Publication No. 10-286235 has disclosed an example of an endoscope equipped with a light source device combining a laser light source which emits three-color laser light of red (R), green (G) and blue (B), an optical fiber, a diffusion plate, and an illumination intensity distribution adjusting filter. Since the optical fiber highly efficiently guides the laser light, a highly efficient and bright light source device can be obtained by this combination of the laser light source and the optical fiber.
The light source device according to Jpn. Pat. Appln. KOKAI Publication No. 10-286235 uses an He—Cd laser light source which is a three-primary-color (white) laser light source for simultaneously emitting a blue laser light having a wavelength of 441.6 nm, a green laser light having a wavelength of 537.8 nm, and a red laser light having a wavelength of 636.0 nm, and an He—Ne laser light source for emitting a red laser light having a wavelength of 632.8 nm. The laser light emitted from these light sources are guided to the distal end of the endoscope by a light guide, and applied to a living body which is an illumination target via the diffusion plate and the illumination intensity distribution adjusting filter.
In general, when the diffused laser light is used as an illumination light, information regarding wavelengths that are not included in the laser light is absent. That is, it is known that when a laser light having a wavelength of 636.0 nm is used as red, red color reproducibility deteriorates if the reflectivity of red having a wavelength of 636.0 nm is considerably different from the reflectivity at other wavelengths. For example, an object which hardly reflects the light having a wavelength in the vicinity of 636.0 nm and which well reflects other light in the red region is observed. In this case, even if the object actually looks red, the object may look dark when a red laser light having a wavelength of 636.0 nm is applied to the object.
Thus, in Jpn. Pat. Appln. KOKAI Publication No. 10-286235, the red laser light source having a wavelength of 632.8 nm is used in addition to the red laser light source having a wavelength of 636.0 nm to improve the red color reproducibility. However, the wavelength difference of the laser light emitted by these light sources is only 3.2 nm. When the wavelength difference is small, not much improvement of color reproducibility can be expected.